Method of proofing and screening color separations using the manifold imaging process



May 19, 1970 v. TULAGIN 3,512,968

METHOD OF PROOFING AND SCREENING COLOR SEPARATIONS USING THE MANIFOLD IMAGING PROCESS Filed July 1, 1965 ACTIVATE SANDWICH APPLY HELD AND EXPOSE SEPARATE FIG. 3B

INVENTOR.

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United States Patent Office 3,512,968 Patented May 19, 1970 3 512 968 METHOD OF PROOFIliG AND SCREENING COLOR SEPARATIONS USING THE MANIFOLD IMAG- ING PROCESS Vsevolod Tulagin, Rochester, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed July 1, 1965, Ser. No. 468,683 Int. Cl. 603g 13/22 U.S. Cl. 961.2 12 Claims ABSTRACT OF THE DISCLOSURE A method of proofing and screening color separations and providing either positive or negative images of said color separations wherein the blue, green and red separations are imaged respectively on yellow, magenta and cyan manifold sets. The positive images obtained from the manifold sets are superimposed to subtractively synthesize a proof of the image.

The present invention relates in general to imaging and, more specifically, to a new system for the formation of high gamma images by layer transfer in image configuration and the use of such a system in color proofing and in the production of color separations.

Although imaging techniques based on layer transfer of a colored material have been known in the past, these techniques have always been clumsy and difficult to operate because they depend upon photochemical reactions and generally involve the use of distinct layer materials for the two functions of image-wise transfer and image coloration. A typical example of the complex structures and sensitive materials employed in prior art techniques is described in U.S. Pat. 3,091,529 to Buskes. Not only does this type of prior art imaging system tend towards complexity in structure in that it employs separate materials for final image coloration and image-wise transfer, but, in addition, image-wise transfer generally depends upon a photo-induced ch mical reaction which changes the adherence of the layer so exposed. The effectiveness of this type of photochemical reaction depends, in turn, upon the vagaries of catalysts used in this system, temperature, pH and many other factors which influence the speed and effectiveness of chemical reactions in general. Many of the prior art systems employ light-sensitive diazo compounds to light. In addition, because of the complexities and critical nature of prior art systems, they are for the most part difiicult and expensive to prepare in the first instance and then can only be used by trained operators. Another problem which has confronted the prior art is that of forming color separations and proofing the s parations prior to making plates for three-color printing. Since color printing is carried out from at least three different plates, each of which is used to print one of the three primary colors, the original colored image must first be separated into its primary color components so that the three plates can be made fronrthese separations.

Somewhere in the process screening is also required since each plate must finally be halftone in order to operate in the printing process. This screening may take place when the separations are first made and is then known as direct screening or the separations may be screened later for proofing and plate making. Since the manufacture of long run color printing plates and their set up in the press is a very expensive and time consuming affair, it is highly desirable to check or proof the image which will be made by the screened separations before the plates are made and set up in the press. The making of these separations and proofing has been expensive and complex in the past because the separations are made in the first instance by exposing the original image to three successive conventional gelatin-silver halide films through three different filters and then processing these films through the conventional silver halide developing and fixing processes. In order to proof these separations, they are used to produce a color positive which will reproduce as closely as possible the three-color image which will be printed when the screened separations are used to make the three plates. This proofing process can be accomplished in several ways, for example, by the use of material sold under the name of Color Key by the Minnesota Mining & Manufacturing Co. or by the use of esp cially made diazo proofing materials. In each case such a proofing procedure involves a separate set of operations, none of which are germane to the main task except as a check on the accuracy of the work.

It is accordingly an object of this invention to provide a new high gamma photographic system;

It is also an object of this invention to provide an imaging system which simultaneously produces a positive and a negative;

A still further object of this invention is to provide an improved system for color proofing;

Yet another object of this invention is to provide an improved system capable of producing color separations and proofs in one simultaneous exposure;

These and still further objects of this invention are accomplished, generally speaking, with a layer of a cohesively weak photoresponsive imaging material on a substrate. These two layers are termed the donor. The imaging layer may then be activated by treating it with a swelling agent or partial solvent for the material, if required to further weaken it. This step may be eliminated, of course, if the layer retains suflicient residual solvent after having been coated on the substrate from a solution or paste. The activating step serves the dual function of making the top surface of the imaging layer slightly tacky and, at the same time, weakening it structurally so that it can be fractured more easily along a sharp line which defines the image to be reproduced. Once the imaging layer is activated, a receiver sheet is laid down over its surface. An electrical field is then applied across this manifold set while it is exposed to a pattern of light and shadow representative of the image to be reproduced. Upon separation of the donor substrate and receiver sheet, the imaging layer fractures along the lines defined by the pattern of light and shadow to which it has been exposed with part of this layer being transferred to the receiver sheet While the remainder is retained on the donor substrate so that a positive image is produced on one while a negative is produced on the other. At least one of the donor substrate and the receiver sheet is transparent and, in fact, both may be transparent so that exposure may be made from either side of the manifold set. The manifold I et may include separate electrodes on opposite sides of the donor substrate and receiver sheet for the application of the field or they may be directly on the back surfaces of these members and integral therewith. In another field application technique, one or both of the donor substrate and receiver sheet may be made of a conductive material. At least one of these is transparent so as to permit exposure of the imaging layer through this electrode. The imaging layer serves the dual function of imparting light sensitivity to the system while at the same time acting as the colorant for the final image produced, although other colorants such as dyes and pigments may be added to it so as to intensify or modify the color of the final images produced when image color is important. The imaging layer may be homogeneous; however, in a preferred form of the invention which has produced superior results a material such as a pigment, which is preferably metal-free phthalocyanine, is dispersed in a cohesively weak insulating binder. Other materials including particles made up of two or more layers, blends of materials, complexes, photoresponsive polymers, etc., may also be dispersed in this type of binder.

In order to proof at the time of screening, the three (or four) separations are screened on different colored manifold sets so that the blue separation is screened on the yellow set, the green separation on a magenta set, the red separation on a cyan set and the black separation on a black set (if a black separation is used). In this way, no matter what type of plate making is used either the negative or the positive sheets of the manifold set automatically provide an immediate proof of the process at that point by superposing these sheets and viewing the transparency thus produced. Direct screening of the separations (as described by F. R. Clapper Improved Colour Separation of Transparencies by Direct Screening J. Phot. Sci. 12, 28 Jan.- Feb. 1964) may also be used in which case the screened separations are merely exposed to the correct manifold set for proofing.

In addition, by providing manifold sets with selective spectral response so that the yellow set responds only to blue light, the magenta set responds only to green light and the cyan set responds only to red light or by using suitable filters with sets which have broader spectral responses these sets may be employed directly to produce the screened separations. This is particularly advantageous in direct screening. The complementary images produced in each of the sets are then superposed for proofing so that color separation, screening and proofing is combined into one quick virtually dry process.

In order that the invention will be clearly understood, reference is now made to the accompanying drawings in which an embodiment of the invention is illustrated by way of example and in which:

FIG. 1 is a side sectional view of a photosensitive imaging member for use in the invention;

FIG. 2 is a side sectional view of a second embodiment of the imaging member;

FIG. 3 is a process flow diagram of the method steps of the invention;

FIGS. 3a and 3b are side sectional views diagrammatically illustrating the process steps of FIG. 3.

Referring now to FIG. 1 of the drawings, there is seen a supporting donor substrate layer 11 and an imaging layer generally designated 12. In the manufacture of the imaging member herein referred to as the manifold set, layer 12 is coated on substrate 11 so that it adheres thereto. These layers are collectively referred to as the imaging donor or merely the donor. In this particular illustrative example, layer 12 consists of photoconductive pigment 13 dispersed in a binder 14. This two-phase system has so far been found to constitute a preferred form for imaging layer 12; however, homogeneous layers made up, for example, of a single component or a solid solution of two or more components are employed where these layers exhibit the desired photoresponse and have the desired physical properties. The basic physical property desired in layer 12 is that it be frangible, having a relatively low level of cohesive strength either in the as-coated condition or after it has been suitably activated as described more fully hereinafter. Since layer 12 serves as the photoresponsive element of the system as well as the colorant in the final image produced, the components of this layer are in most cases preferably selected so as to have a high level of photoresponse while at the same time being intensely colored so that a high contrast image can be formed by the high gamma system of the invention. Thus, for example, in the two-phase system intensely colored photo responsive pigments such as phthalocyanine blues, quinacridone reds and the like are preferred. The alpha and X crystalline forms of metal-free phthalocyanine are especially preferred pigments for use in the invention because of their very high sensitivity. The X crystalline form is described in copending application No. 375,191, filed June 15, 1964 now abandoned, and entitled Electrophotographic Element. It is to be understood, however, that since the binder itself may be dyed or pigmented with additional colorant in either the single-phase or twophase system, intense coloration of the photoresponsive material itself, while being preferred, is not critical in any sense even for high contrast imaging. Accordingly, even transparent materials may be used.

The main characterizing property of the system is that it is essentially a go or no go system, so that the imaging layer either stays on the donor substrate or transfers to the receiver sheet. In those instances where topography or surface configuration of the image is most important, e.g., manufacture of printing plates, or resist patterns for printed circuits, the difference between the maximum density of the imaging layer and the substrate or receiver sheet upon which it is supported after imaging may be very small because of the use of a relatively transparent imaging layer. However, where there is any difference at all between these densities, the system may be defined as a high gamma system; that is, one in which the slope of the density vs. log of exposure curve is very large in that portion of the curve where the imaging layer responds.

It is, accordingly, to be understood that any suitable photoresponsive material may be employed in this system with the choice depending largely upon the photosensitivity required, the spectral sensitivity, the degree of contrast desired in the final image, whether a heterogeneous or a homogeneous system is desired and similar considerations. Typical photoconductors include substituted and unsubstituted phthalocyanine, quinacridones, zinc oxide, mercuric sulfide, Algol yellow (Cl. No. 67,300), cadmium sulfide, cadmium selenide, Indofast brilliant scarlet toner (C.I. No. 71,140), zinc sulfide, selenium, antimony sulfide, mercuric oxide, indium trisulfide, titanium dioxide, arsenic sulfide, Pb O gallium triselenide, zinc cadimum sulfide, lead iodide, lead selenide, lead sulfide, lead telluride, lead chromate, gallium telluride, mercuric selenide, and the iodides, sulfides, selenides and tellurides of bismuth aluminum and molybdenum. Others include the more soluble organic photoconductors (which facilitate the fabrication of homogeneous systems) especially when these are complexed with small amounts (up to about 5%) of suitable Lewis acid-s. Typical of these organic photoconductors are 4,5 -diphenylimidazolidinone;

4,5 -diphenylimidazolidinethione;

4,5 -bis- 4'-amino-phenyl) -imidazolidinone;

1,5-cyanonaphthalene;

1,4-dicyanonaphthalene;

aminophthalodinitrile;

nitrophthalidinitrile;

1,2,5 ,6-tetraazacyclooctatetraene- 2,4,6,8

3 ,4-di- 4-methoxyphenyl) -7,9-diphenyl- 1,2,5 ,6-tetraazacyclooctatetraene- (2,4,6,8

3 ,4di- (4'-phenoxyphenyl) 7,8-diphenyl-1,2,5,6-tetraazacyclooctatetraene- (2,4,6,8)

3 ,4,7, S-tetramethoxy-1,2,5,6-tetraaza-cycloactatetraene- Z-mercapto-benzthiazole;

Z-phenyl-4-diphenylidene-oxazolone;

2-phenyl-4-p-methoxy-b enzylidene-oxazolone;

6-hydroxy-2-phenyl-3 (p-dimethylamino phenyl -benzofurane;

6-hydroxy-2,3 -di (p-methoxyphenyl -benzofurane;

2,3 ,5 ,6-tetrap-methoxyphenyl) -furo- 3 ,2f -benzofurane;

4-dimethylamino-benzylidene-benzhydrazide;

4-dimethylaminobenzylidene-isonicotinic acid hydrazide;

furfurylidene-(2,4'-dimethyl-amino-benzhydrazide);

S-benzilidene-aminoacenaphthene;

3-benzylidene-amino-carbazole;

(4-N,N-dimethylan1inobenzylidene) -p-N,N-d1methylaminoaniline;

(2-nitro-benzylidene -p-bromo-anil1ne;

N,N-dimethyl-N-(2-nitro-4-cyano-benzyl1dene) -pphenylene-diamine;

2,4xliphenyl-quinazoline;

2-(4-amino-phenyl)-4-phenyl-qumazol1ne;

2-phenyl-4- (4'-di-methyl-amino-phenyl) -7-methoxyquinazoline;

l,3-diphenyl-tetrahydrolmldazole;

1,3-di- (4-chlorophenyl) -tetrahydro-1m1dazole;

1,3-diphenyl) -2,4'-dimethyl-amlno-phenyl) -tetrahydroimidazole; D

3- (4'-dimethylamino-phenyl -5- (4"-methoxy-phenylen 1 -1,2,4-triazine;

3-p yi i dil-i 4 -5-(4"-dimethylamino-phenyl) -6-phenyl- 1,2,4-trizine; I

3-(4'-aminIo-phenyl) -5,6,-di-phenyl-1,2,4-tr1az1ne,

2,5 -bis [4- (N-ethyl-N-acetyl-amino) -phenyl-( 1 1,3 ,4-triazole;

1,5 -diphenyl-3 -me{hyl-pyrit zohne;

- etra hen azo me;

lfiriiil nila- 3'4'11il iy droxy-methylene-phenyl) benzimidazole;

2-(4-dimethylamino-phenyl)benzoxazole;

2- (4-methoxyphenyl) -benzth1azole; I

2,5-bis-[p-aminophenyl-(1)]-1,3,4-ox1dazole,

4,5 diphenyl-imidazolone S-aminocarbazole;

copolymers and mixtures thereof. Any suitabe Lei: acid (electron acceptor) may be employed un erfigned plexing conditions with many of the aforemen of more soluble organic materials and also with many the more insoluble organics to impart very rmportan an} creases in photosensitivity to those materials. 532px:- Lewis acids are 2,4,7-trinitro-9-fluorenone; 2 4.56 c He nitro-9-fluorenone; picric ac1d; l,?,5 tnmtro e nze e chloranil; benzo-quinone; 2,5 dICI IlOIO-bEHZOqUlIIOIIJIe: 2 6 dichlorobenzo-quinone; chloranil; naphthocpgnoui' (l,4); 2,3 dichloronaphthoqmnone (1,4), lat; flagranone; 2 methyl-anthraqulnone; 1,4 drmet y-a2 car quinone; 1 chloroanthraqumone; anthraqumongoroltboxylic acid; 1,5 dichloroanthraqumone, 1 0 themenitroanthraquinone; PheIlanthlfillglcglllgzeu?ggfigp thicquinone; pyranthrenequino ne; 8 d l-fonic aid and napthenequinone; anthraqumonel, t-hislu LbenZene-aldeanthraquinone 2 aldehyde; triph a 0y;1 d 2 6 dih des such as bromal, 4 mtrobenzalde y e,- ili'ilfi illiiiliilfiiliicene-9-aldehyde; pyrene- -a e ,14 ldehyde Organi pyridine-2,6 dialdehyde, blpheny giro-benZAne-Phosphosphonic acids such as 4-ch oro- Ar-nitmPhenol and phonic acid; nitrophenols, such as am 16 acetic anhypicric acid; acid anhydride-s; for ex nhpdgide phthalic succinic anhydnde, malerc a i y l lliidllde; tetrachlorophthalic anhydride, 3pgrglteieac3i, 9yloitetracarbgxydlic d b ro ir i o i lie iZ aiid anhydride; boxylic anhy r1 e; 1- f the roups f the metals and metalloids o g l l f ll lln iigli to group VIII of the perciglclolrciadle syfsielrrii e: aluminum chlori e, z1nc ililofi di iiii tetrachloride, (stannic chloride); agrsefiffi'g chloride stannous chloride, antlmony ipenl ac bro: magnesium chloride; magneslum bronnde, ca clum bro. mide; calcium iodide; strontium bromide; chromic mide; manganous chloride; cobaltous chloride; cobaltic chloride; cupric bromide; ceric chloride; thorium chloride; arsenic triiodide; boron halide compounds, for example: boron trifluoride and boron tnchlonde; and ketones, such as acetophenone benzophenone; 2 acetylnaphthalene; benzil; benzoin; S-benzoyl acenaphthene; biacene-dione; 9-acetyl-anthracene; 9-benzoyl-anthracene; 4 (4 dimethylamino cinnamoyl) 1 acetylbenzene; acetoacetic acid anilide; indandi'one-(1,3)-(l-3-diketohydrindene); acenaphthene quinonedichloride; anisil, 2,2- pyridil; furil; mineral acids such as the hydrogen halides, sulphuric acid and phosphoric acid; organic carboxylic acids, such as acetic acid and the substitution products thereof; monochloro-acetic acid; dichloro acetic acid; trichloro-acetic acid; phenylacetic acid; and G-methylcoumarinylacetic acid (4); maleic acid, cinnamic acid; benzoic acid; l-(4-diethyl-aminobenzoyl)-benzene-2-carboxylic acid; phthalic acid; and tetrachlorophthalic acid; alpha beta di bromo beta-formyl-acrylic acid (mucobromic acid); dibromo-maleic acid; 2-bromo-benzoic acid; gallic acid; 3-nitro-2-hydroxyl-l-benzoic acid; Z-nitro phenoxy-acetic acid; 2-nitro-benzoic acid; 3- nitro benzoic acid; 4-nitro-benzoic acid; 3-nitro-4-ethoxybenzoic acid; 2-chl0ro-4-nitro-l-benzoic acid; 2 chloro- 4-nitro-1-benzoic acid; 3 nitro-4-methyl-benzoic acid; 4-nitro-l-methyl-benzoic acid; 2-chloro-5-nitro-l-benzoic acid; 3-chloro-6-nitro-l-benzoic acid; 4-chlor0-3-nitro-1- benzoic acid; 5-chloro-3-nitro2-hydroxy-benzoic acid; 4-chloro-2-hydroxy-benzoic acid; 2,4 dinitro-l-benzoic acid; 2-bromo-5-nitro-benzoic acid; 4-chlorophenyl-acetic acid; 2-chloro-cinnamic acid; Z-cyano-cinnamic acid; 2,4-dichlorobenzoic acid; 3,5-dinitro-benzoic acid; 3,5- dinitro-salycylic acid; malonic acid; mucic acid; acetosalycylic acid; benzilic acid; butane-tetra-carboxylic acid; citric acid; cyano-acetic acid; cyclo-hexane-dicarboxylic acid; cyclo-hexene-carboxlic acid; 9,10-dichloro-stearic acid; fumaric acid; itaconic acid; levulinic acid; (levulic acid); malic acid; succinic acid; alpha-bromo-stearic acid; citraconic acid; dibromo-succinic acid; pyrene- 2,3,7,8-tetra-carboxylic acid; tartaric acid; organic sulphonic acids, such as 4-toluene sulphonic acid; and benzene sulphonic acid; 2,4-dinitro-l-methyl-benzene-G-sulphonic acid; 2,6-dinitro-1-hydroxy-benzene-4-sulphonic acid and mixtures thereof.

In addition, other photoconductors may be formed by complexing one or more suitable Lewis acids with poly mers which are ordinarily not thought of as photoconductors. Typical polymers which may be complexcd in this manner include the following illustrative materials: polyethylene terephthalate, polyamides, polyimides, polycarbonates, polyacrylates, polymethylmethacrylates, polyvinyl fluorides, polyvinyl chlorides, polyvinyl acetates, polystyrene, styrene-butadiene copolymers, polymethacrylates, silicone resins, chlorinated rubber, and mixtures and copolymers thereof Where applicable; thermosetting resins such as epoxy resins, phenoxy resins, phenolics, epoxy-phenolic copolymers, epoxy ureaformaldehyde copolymers, epoxy melamine-formaldehyde copolymers and mixtures thereof, where applicable. Other typical resins are epoxy esters, vinyl epoxy resins, tall-oil modified epoxies, and mixtures thereof Where applicable.

It is also to be understood in connection with the heterogeneous system, that the photoconductive particles themselves may consist of any suitable one or more of aforementioned photoconductors, either organic or inorganic, dispersed in, in solid solution in, or copolymerized with, any suitable insulating resin whether or not the resin itself is photoconductive. This particular type of particle may be particularly desirable to facilitate dispersion of the particle, to prevent undesirable reac tions between the binder 14 and the photoconductor or between the photoconductor and the activator and for similar purposes. Typical resins of this type include polyethylene, polypropylene, polyamides, polymethacrylates, polyacrylates, polyvinyl chlorides, polyvinyl acetates, olystyrene, polysilixoxanes, chlorinated rubbers, polyacrylonitrile, epoxies, phenolics, hydrocarbon resins and other natural resins such as rosin derivatives as well as mixtures and copolymers thereof.

The ratio of photoconductor 13 to binder 14 by volume in the heterogeneous system may range from about to 1 to about 1 to 10, but it is generally been found that proportions in the range of from about 1 to 2 to about 2 to I produce the best results and, accordingly, this constitute-s a preferred range.

As stated above, imaging layer 12 has relatively low cohesive strength either in the as-coated condition or after it has been suitably activated. This, of course, is true for both the homogeneous system and the heterogeneous system. One technique for achieving low cohesive strength in the layer 12 is to employ relatively weak, low molecular weight materials therein. Thus, for example, in a single component homogeneous layer 12 a monomeric compound or a low molecular weight polymer complexed with a Lewis acid to impart a high level of photoresponse to the layer may be employed. Similarly when a homogeneous layer utilizing two or more components in solid solution is selected to make up layer 12, either one or both of the components of the solid solution may be a low molecular Weight material so that the layer has the desired low level of cohesive strength. This approach may also be taken in connection with the heterogeneous layer 12 illustrated in FIG. 1. Although the binder material 14 in the heterogeneous system may in itself be photoresponsive, it does not necessarily have this property so that minerals such as microcrystalline wax, paraffin wax, low molecular weight polyethylene and other low molecular weight polymers may be selected for use as this binder material solely on the basis of physical properties and the fact that they are insulating materials without regard to their photoresponse. This is also true of the two-component homogeneous system where non-photoresponsive materials with the desired physical properties can be used in solid solution with photoresponsive material. Any other technique for achieving low cohesive strength in imaging layer 12 may also be employed. For example, suitable blends of incompatible materials such as a blend of a polysiloxane resin with a polyacrylic ester resin may be used either as binder layer 14 in a heterogeneous system or in conjunction with a homogeneous system in which the photoresponsive material may be either one of the incompatible components (complexed with a Lewis acid) or a separate and additional component of the layer. The thickness of imaging layer 12 is not critical and layers from about 0.5 to about 10 microns have been used.

Above imaging layer 12 is a third or receiving layer 16. This receiver sheet is ordinarily supplied as a separate layer which does not initially adhere to layer 12. Accordingly, although the whole imaging member or manifold set may be supplied in a convenient threelayer sandwich as shown in FIG. 1, receiving layer 16 may also be supplied as a separate sheet or roll if desired. On the other hand, in those systems where activation of the imaging layer is not required or where imaging layer 12 has been preactivated at the factory, layer 16 adheres to or is at least tacked onto imaging layer 12. In the particular embodiment of the manifold set shown in FIG. 1, both the donor substrate 11 and the receiver sheet 16 are made up of an electrically conductive material such as cellophane with at least one of them being optically transparent to provide for the exposure of layer 12. There should be a fairly close balance between the adherence of imaging layer 12 for the donor and receiver layers 11 and 16, respectively, with a slightly stronger adherence to the donor at the time of imaging. Accordingly, layers 11 and 16 should be selected with this in mind. One way to easily accomplish this balance is to use the same material for layer 16 as is used for layer 11.

Although the structure of FIG. 1 represents one of the simplest forms which the manifold set may take, another embodiment is illustrated in FIG. 2 where imaging layer 12 may take any one of the forms as described above in connection with FIG. 1. In the FIG. 2 embodiment imaging layer 12 is deposited on an insulating donor substrate 17 which is backed with a conductive electrode layer 18 while the image receiving portion of the manifold set also consists of an insulating receiver sheet 19 backed with a conductive electrode layer 21. Here again either or both of the pairs of layers 17-18 and layers 1921 may be transparent so as to permit exposure of imaging layer 12. Flexible, transparent conductive materials, such as cellophane which may be used in the FIG. 1 embodi ment of the invention are, for the most part, relatively weak materials with the choice of these materials being quite limited. The FIG. 2 structure which uses an insulating donor substrate and receiver sheet 17 and 19, respectively, allows for the use of high strength insulating polymers such as polyethylene, polypropylene, olyethylene terephthalate, cellulose acetate, Saran (vinyl chloridevinylidene chloride copolymer) and the like. Not only does the use of this type of high strength polymer provide a strong substrate for the positive and negative images formed on the donor substrate and receiver sheet, but in addition, it provides an electrical barrier between the electrodes and the imaging layer 12 which tends to inhibit electrical breakdown of the system. Combinations of the structure described in FIGS. 1 and 2 may also be used in carrying out the invention with a relatively conductive layer immediately in contact with one side of imaging layer 12 and a conductively backed insulating layer on the other side of the imaging layer.

Referring now to the flow diagram of FIG. 3 it is seen that the first step in the imaging process is the activation step. In this stage of the imaging process, the manifold set is opened and the activator is applied to imaging layer 12 following which these layers are closed back together again as indicated in the second block of the process flow diagram of FIG. 3. Although the activator may be applied by any suitable technique such as with a brush, with a smooth or rough surfaced roller, by flow coating, by vapor condensation or the like, FIG. 3a which diagramatically illustrates the first two process steps shows the activator fluid 23 being sprayed on to imaging layer 12 of the manifold set from a container 24. Following the deposition of this activator fluid, the set is closed by a roller 26 which also serves to squeegee out any excess activator fluid which may have been deposited. The activator serves to create an adhesive bond between imaging layer 12 and receiver sheet 16 as Well as to swell or otherwise weaken and thereby lower the cohesive strength of imaging layer 12. The activator should also have a high level of resistivity so that it will not provide an electrically conductive path through imaging layer 12 and in addition so that the imaging layer will support the electrical field which is applied through it during the exposure. Accordingly, it will generally be found to be desirable to purify commercial grades of activators so as to remove impurities which might impart a higher level of conductivity to the activating fluids. This may be accomplished by running the fluids through a clay column or by any other suitable purification technique. Generally speaking, the activator may consist of any suitable solvent having the aforementioned properties and which has the above-described effect on imaging layer 12. For purposes of this specification and the appended claims the term solvent shall be understood to include not only materials which are conventionally throught of as solvents but also those which are thought of as partial solvents, swelling agents or softening agents for imaging layer 12. It is generally preferable that the activator solvents have a relatively low boiling point so that fixing can be accomplished after image formation by solvent evaporation with mild heating at most. It is to be understood, however, that the invention is not limited to the use of these relatively volatile activators. In fact, very high boiling point non-volatile activators including silicone oils such as dimethyl-polysiloxanes and very high boiling point long chain aliphatic hydrocarbon oils ordinarily used as transformer oils such as Wemco-C transformer oil available from Westinghouse Electric Co. have also been successfully utilized in the imaging process. Although these less volatile activators do not dry off by evaporation, image fixing can be ac complished by rolling off the final image produced on an absorbent sheet such as paper which soaks up the activator fiuid. In short, any suitable volatile or non-volatile solvent activator may be employed. Typical solvent include Sohio odorless solvent 3440 an aliphatic (kerosene) hydrocarbon fraction available from Standard Oil Co. of Ohio, carbon tetrachloride, petroleum ether, Freon 214 (tetrafluorotetrachloropropane) other halogenated hydrocarbons such as chloroform, methylene chloride, trichloroethylene, perchloroethylene, chlorobenzene, trichloromonofluoromethane, tetrachlorodifluoroethane, trichlorotrifluoroethane, amides such as formamide, dimethyl formamide, esters such as ethyl acetate, isopropyl acetate, butyl acetate, amyl acetate, cyclohexyl acetate, isobutyl propionate and butyl lactate, ethers such as diethyl ether, diisopropyl ether, dioxane, tetrahydrofuran, ethyleneglycol monoethyl ether, aromatic and aliphatic hydrocarbons such as benzene, toluene, Xylene, hexane, cyclohexane, gasoline, mineral spirits and white mineral oil, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone and vegetable oils such as coconut oil, babussu oil, palm oil, olive oil, castor oil, peanut oil and neatsfoot oil and mixtures thereof.

In certain instances the first two steps of the imaging process, as diagramatically illustrated in FIG. 3a, may be omitted. Thus, for example, a manifold set which is preactivated at the factory may be supplied or if imaging layer 12 is initially fabricated to have a low enough cohesive strength, activation may be omitted and receiving layer 16 may be adhered to the surface of imaging layer 12 at the time when that layer is coated on substrate 11 either from solution or from a hot melt. It is generally preferable, however, to include an activation step in the imaging process because if this step is included then a stronger and more permanent imaging layer 12 may be provided which can withstand storage and transportation prior to imaging and which will provide a more permanent final image after imaging.

Once the proper physical properties have been imparted to imaging layer 12 and the receiving sheet 16 has been adhered to its upper surface, an electrical field is applied across the manifold set and it its exposed to the image to be reproduced. Upon separation of substrate 11 and receiving sheet 16, imaging layer 12 fractures along the edges of exposed areas and the surface where it is adhered to either substrate 11 or receiving sheet 16. Accordingly, once separation is complete, exposed portions of imaging layer 12 are retained on one of layers 11 and 16 while unexposed portions are retained on the other layer, resulting in the simultaneous formation of a high gamma positive image on one of those sheets and a high gamma negative on the other. Whether exposed portions are retained on donor substrate 11 or transferred to receiver sheets 16 will, of course, depend on the particular photoresponsive material employed in the irnaging member as well'as the polarity of the applied field. By making the initial degree of adherence of layer 12 only slightly higher for layer 11 than for layer 16, imaging layer 12 is finally retained on layer 11 unless the combined effect of exposure and applied field are added to the bond strength of layers 11 and 12, thereby exceeding the strength of the bond between layers 12 and 16. In this way an amplification effect is achieved and transfer may be caused with relatively low levels of light exposure. The application of the required electrical field is relativey straightforward; however, with some materials there is a preferred polarity orientation. Thus, for

example, with an imaging layer made up of finely divided metal-free phthalocyanine particles dispersed in a microcrystalline wax, the best images are formed when the donor is positioned at the illuminated electrode which is made negative and the non-illuminated electrode is positive. The reversal of this polarity generally results in a poorer image or lower sensitivity and sometimes in a reversal of position in that a duplicate of the exposed original is formed on the non-illuminated side of the manifold set instead of at the illuminated side which is the usual case. Accordingly, potential source 28, shown in FIG. 3b, is indicated as having its negative side connected to substrate 18 through which exposure is made by light rays 29. Preferred field strengths are in the range of about 1,500 to 2,000 volts per mil. across the manifold set. Thus, using 2 mil. Mylar sheets for both donor substrate and receiver sheet, the preferred applied voltage is 6,000 to 8,000 volts across the electrodes outside these Mylar sheets. However, suitable images are also produced with voltages of from about 4,000 to about 10,000 volts. In general, the receiver sheet is rolled down onto the activated imaging layer 12 with the power on. However, to prevent air gap breakdown at the nip which will result in the production of Lichtenberg patterns, a fairly large resistance is preferably inserted in series with the power supply to limit the flow of current and the rate of charging of the capacitor which the manifold set forms. A fairly large resistor on the order of from about at least 5,000 to 20,000 megohms satisfactorily performs this function although the largest value resistors lower the gamma somewhat. This resistance may be omitted if sheet closure occurs before the field is applied. However, even then the resistor is preferably retained in the circuit to provide protection for the operator and limit the energy in a spark when occasional breakdown occurs in flaws or pinholes in the Mylar. Another important function of this resistor, which is shown as resistor 30 in FIG. 3b, is that it provides a path for discharging the capacitor at an adequate rate to prevent sparking during separation of the donor and the receiver sheet.

A visible light source, an ultraviolet light source or any other suitable source of actinic electromagnetic radiation may be used to expose the manifold set of this invention. Better quality images are produced by exposing from the donor side of the imaging layer and, accordingly, the receiver sheet 16 is usually separated from the other layers of the manifold set just after image exposure and generally with the power on both electrodes. This operation involves a current flow because as the layers are separated, the capacitance of the manifold set is reduced and charge stored in this capacitor is caused to flow back through the resistor in the circuit which dissipates this current as in PR heat loss. Short delays in separation after the exposure step seem to have no deleterious effects on the images produced. Essentially the same result is produced if separation occurs after the power is turned off because the charge stored in the capacitor which is formed by the manifold set still applies a field across the imaging layer but generally poorer images result. It is to be noted that even when the power supply is turned off, it still acts as part of a closed circuit connecting the resistor to the two electrodes of the manifold set because of the LC filter network in the output of this type power supply. It is believed that a charge differential is built up between exposed and unexposed areas of layer 12 during the process so that when layers 11 and 16 are separated, the applied field causes imagewise portions of layer 12 to go with receiver 16 While the complementary or background areas are retained on layer 11 to which layer 12 adheres more strongly.

If a relatively volatile activator is employed, such as petroleum ether or carbon tetrachloride, Freon 215, fixing occurs almost instantaneously after separation of the layer because the relatively small quantity of activator in the 2-5 micron layer of imaging material flashes off very rapidly. With somewhat less volatile activators, such as the Sohio odorless solvent 3440 or Freon 214 described above, fixing may be accelerated by blowing air over the images or warming them to about 150 F., whereas with the even less volatile activators, such as transformer oil, fixing is accomplished by absorption of the activator into another layer such as paper substrate to which the image is transferred. Many other fixing techniques and methods for protecting the images such as overcoating, laminating with a transparent thermoplastic sheet and the like will occur to those skilled in the art. Increased image durability and hardness may also be achieved by treatment with an image material hardening agent or with a hard polymer solution which will wet the image material but not the donor substrate.

In general, the apparatus for carrying out the imaging procedure described above will employ the elements illustrated in FIGS. 3a and 3b including a source of activator fluid, a squeegee roller to remove excess activator fluid, a power supply with series resistor and a set of electrodes which may or may not be built in to the manifold set. Opening the manifold set for activation, closing the set for exposure and opening again for separation and image formation may be accomplished by an one of a number of techniques which will be obvious to those skilled in the art. However, one straightforward way to accomplish this result is to supply the imaging materials in the form of long webs which can be entrained over rollers so as to provide opening and closing of the set during the imaging process.

It is to be noted that as pointed out supra manifold sets may be supplied in any color desired either by taking advantage of the natural color of the photoresponsive or binder materials in the imaging layer of the manifold set or by the use of additional dyes and pigments therein whether photoresponsive or not, and, of course, various combinations of these photoresponsive and nonphotoresponsive colorants may be used in the imaging layer so as to produce the desired color. Although manifold images are in the form of transparencies when first produced, these images may be laminated with opaque backing material of various contrasting colors to produce prints. In addition, manifold images using different colored imaging layers such as cyan, magenta and yellow may be combined to produce tfull natural color images by super position of transparencies. It is also to be noted that different photoresponsive materials have different spectral responses and that the spectral response of many photoresponsive materials may be modified by dye sensitization so as to either increase and narrow the spectral response of a material to a peak or to broaden it to make it more panchromatic in its response. Thus, the material can be used to make ordinary black and white images using panchromatic response while narrow spectral response materials may be employed for the production of color separations or the like.

In proofing color separations, the blue separation is screened on a yellow manifold set, the green separation on a magenta manifold set, the red separation on a cyan manifold set, and the black separation on a black manifold set. In this way no matter what type of plate making technique is used either the negative or positive sheets of the three sets automatically provide an immediate proof of the process at that point when they are superpositioned and viewed as a transparency. In this case the manifold sets need not necessarily have peaked spectral responses so long as they show response to the color of light of the particular separation to which they are exposed. In another technique, however, where the manifold sets are used both to produce the separations and the proofs, the yellow, magenta and cyan sets respond, respectively, to blue, green and red light only. In this way no filter is required since each set only responds to the desired color of color reproducing this light image in its complementary color. In another technique, sets with broader spectral response are exposed with filters. At the same time that the color separations are being produced from one side of the manifold set, the proofing transparencies are produced by the complementary images on the other side of the manifold sets and proofing is again accomplished by merely superposing the transparencies and viewing them together.

The invention having been generally described above, specific preferred embodiments of the invention are given in the following examples. All parts in the examples are taken by weight unless otherwise indicated.

EXAMPLES I-IV A commercial, metal-free phthalocyanine is first purified by acetone extraction to remove organic impurities. Since this extraction step yields the less sensitive beta crystalline form, the 100 grams desired alpha form is obtained by dissolving 100 g. of the beta in 600 cc. of sulfuric acid, and precipitating it by pouring the solution into 3,000 cc. of ice water and washing with water to neutrality. The thus purified alpha phthalocyanine is then salt milled for 6 days and desalted by slurrying in distilled water, vacuum filtering, water washing and finally methanol washing until the initial filtrate is clear. After vacuum drying to remove residual methanol, the X-form phthalocyanine thus produced is used to prepare the imaging layer according to the following procedure: 5 grams of Sunoco 1290, a microcrystalline wax with a melting point of 178 F. is dissolved in 100 cc. of reagent grade petroleum ether heated to 50 C. and quenched immersing the container in cold water to form small wax crystals. Five grames of the purified and milled phthalocyanine produced according to the above procedure are then added to the wax paste along with /2 pint of clean porcelain balls in a 1 pint mill jar. This formulation is then ball milled in darkness for 3 /2 hours at 70 r.p.m. and after milling 20 cc. of Sohio solvent 3440 is added to the paste. This paste is then coated in subdued green light on a 2 mil. Mylar sheet with a No. 12 wire-wound drawdown rod which produces a 2.5 micron thick coating after drying. The same paste is also applied on three other Mylar sheets with a No. 8 drawdown rod to produce a coating thickness of 1 /2 microns, with a No. 24 rod to produce a coating thickness of 5 microns and a No. 36 rod to produce a coating thickness of 7 /2 microns. Each of these coatings is then heated to about 140 F. in darkness in order to dry it. Then the coated donors are placed on the tin oxide surface of NESA glass plates with their coatings facing away from the tin oxide. A receiver sheet also of 2 mil. thick Mylar is then placed on the coated surface of each donor. Then a sheet of black, electrically conductive paper is placed over the receiver sheet to form the complete manifold set. The receiver sheet is then lifted up and the phthalocyanine wax layer is activated with one quick brush stroke of a wide camels hair brush saturated with petroleum ether. The receiver sheet is then lowered back down and a roller is rolled slowly once over the closed manifold set with light pressure to remove excess petroleum ether. The negative terminal of an 8,000 volt DC. power supply is then connected to the NESA coating in series with a 5,500 megohm resistor and the positive terminal is connected to the black opaque electrode and grounded. With the voltage applied a white incandescent light image is projected upward through the NESA glass using a Wollensak mm., f4.5 enlarger lens with illumination of approximately 1/ foot-candle applied for 5 seconds for a total incident energy of 0.05 foot-candle-seconds. After exposure, the receiver sheet is peeled from the set with the potential source still connected. The small amount of petroleum ether present evaporates within a second or so after separation of the sheets yielding a pair of excellent quality images with a duplicate of the original on the donor sheet and a reversal of the original on the receiver sheet. All four coating thicknesses produce good quality images; however, it is apparent that there is a slight increase in sensitivity and gamma with increasing thickness of the phthalocyanine wax coating. Example VIII. When these donors are imaged accordin Example VI, 1 to 5 in Example VII and 1 to in ing to the procedure of Example I, all produce dense high resolution images with the exception of Example VIII which produces a coating of lower reflection density and noticeably lower resolution.

EXAMPLES V-VIII Five donor substrates are coated according to the procedure of Example I except that the ratio of phthalocyanme pigment to wax is 5 to 1 in Example V, 1 to 4 EXAMPLES IX-XIII The procedure of Example I is repeated except that the phthalocyanine pigment is mixed at a ratio of 1 to 1 for each of the following binders: for Example IX Sunoco microcrystalline wax grade 5 825 having an ASTM-D- 127 melting point of 151 F. is used; for Example X grade 985, another Sunoco microcrystalline wax having a melting point of 193 F. is used; for Example XI Sunoco paraflin wax, grade 5512, having a melting point of 153 F. (ASTM-D-87) is used; for Example XII a low molecular weight polyethylene sold by Eastman Chemical Products Inc. under the tradename Epolene C-12 having an approximate molecular weight of 3,700, a ring and ball softening point of 92 C., an acid number of 0.05 and a density at 25 C. of 0.893 is used; for Example XIII grade N-ll of the Epolene low molecular weight polyethylene series is employed having an approximate molecular weight of 1,500, a ring and ball softening point of 107 C., a density at 25 C. of .924 and an acid number of 0.05. Each of these coatings is imaged according to the procedure of Example I and all are found to produce good quality images although Sunoco 5825 microcrystalline wax of Example IX and 5512 paraflin wax of Example XI produce some blue haze in the background of the image which remains on the donor apparently because of the fact that these waxes are softer than the other materials tested.

EXAMPLES XIV-XVIII Five donors are prepared according to the procedure of Example I and images according to the procedure given in that example with the exception that the following activators used in each of the examples. In Example XIV it is activated with Sohio odorless solvent 3440, Example XV is activated with carbon tetrachloride, Example XVI is activated with Freon 214 (tetrachlorotetrafluoropropane), Example XVII is activated with Dow-Corning silicone oil D0200 (dimethylpolysiloxane), and Example XVIII is activated with Wemco-C transfer oil, a very high boiling point long chain aliphatic oil available from Westinghouse Electric. In each of these examples, the activators produce a high quality image upon separation. In the case of Examples XIV-XVI, the final images require mild heating at most to dry ofi the activator and harden the image, while in the case of Examples XVII and XVIII the non-drying activator maintains the image in a wet condition. These two images are then rolled off on an absorbent paper substrate which picks up most of the activator thereby hardening the imaging material on the surface.

EXAMPLES XIX-XXIV In Examples XIX-XXIV six doners are made according to the procedure of Example I and the imaging procedure of Example I is followed with the only exception that the pigment used in forming the imaging layer is as follows: in Example XIX the stabilized alpha crystalline form of metal-free phthalocyanine is employed. This material is prepared by acetone extraction of the commercial metalfree phthalocyanine and sulfuric acid solution reprecipitation of the extracted material as in Example I followed by neat milling for one day of the precipitated material in a porcelain mill with Burundum balls. This milling stabilizes the alpha for-m conversion to the beta form. In Example XX the beta form of metal-free phthalocyanine is used. This is produced by the same acetone extraction and precipitation from sulfuric acid solution with no milling. In Example XXI Algol yellow GC Color Index No. 67,300 (l,2,5,6-di(C,C'-diphenyl) thiazole anthraquinone) is used. In Example XXII the pigment used is 2,9-dimethylquinacn'done. In Example XXIII, French process zinc oxide is used as the pigment. In Example XXIV mercuric sulfide is used as the pigment. While all of these materials produce images, it is found that the stabilized alpha phthalocyanine of Example XIX has about one order lower sensitivity as the X-crystal form of Example I While the beta phthalocyanine is about two orders of magni- EXAMPLES XXV-XXVIII Four imaging members or manifold sets are made up and imaged according to the procedure of Example I with the exception that various electrodes, donor substrates and receivers are employed as follows:

Example Base Donor Receiver Upper No electrode substrate sheet electrode XXV Cellophane Electrode. Electrode Cellophane. XXl/I .do Mylar .do Do. XXVII. NE SA Cellulose Cellulose Conductive glass. acetate. acetate. black paper aluminum.

Each of these structures produce results which are about equivalent to those of the Example I procedure.

EXAMPLE XXIX Eight parts by weight of 2,5-bis (p-aminophenyD- 1,3,4-oxidiazole and 12 parts by weight of Lucite 2008, a low molecular weight polymethyhnethacrylate available from E. I. du Pont & Co. are dissolved in parts by weight of methylethyl ketone along with 0.25 part by weight of bromphenol blue dye. This solution is then coated on a 2 mil. Mylar substrate and before the coating is fully dried it is dipped in a water bath which dilutes the solution causing the solids to precipitate out in a weak semi-particulate form in which the individual particles are bonded at their interfaces much like a sintered layer. The donor thus prepared is imaged according to the procedure of Example I with Mylar receiver sheet beneath'an electrically conductive black paper electrode and using a transparent NESA glass electrode beneath the Mylar layer of the donor. Although the dye increases the sensitivity of the layer somewhat and imparts a pink tinge to it, both the sensitivity of the system and the resolution of the image produced are lower than that of the system of Example I.

EXAMPLE XXX Twenty parts by weight of polyvinylcarbarzole is dissolved in 80 parts by weight of toluene along with 2 parts by weight of a 2,4,7-trinitro-9-fluorenone charge transfer complexing agent and 005 part by weight of a bromphenol blue sensitizing dye. After partial drying of the coating, it is dipped in acetone which causes precipitation of the solids from solution in the same type of physical structure as described above in connection with Example XXIX. This donor is imaged according to the same procedure as used in connection with Example XXIX and is somewhat more sensitive than the coating of Example XXIX.

1 5 EXAMPLE XXXI Three manifold sets made with yellow, cyan and magenta pigments, as described in Examples XXI, XIX and XXII, respectively, are made up and imaged according to the procedure of those examples. The yellow, cyan and magenta manifold sets are exposed through a screen to the blue, red and green color separations formed from a colored original. Upon separation of the manifold sets the positive images are superimposed with the yellow on the bottom followed by the magneta and cyan positives so that a screened proof is provided. At the same time the three screened negatives formed on separation of the manifolds are ready for use in making the plates providing the proof is satisfactory. It is accordingly seen that the proofs are made simultaneously with the formation of the screened negatives.

What is claimed is:

1. A method of proofing color separations comprising forming positive images by imaging with actinic electromagnetic radiation the blue, green and red separations from a color image respectively on yellow, magenta and cyan cohesively weak, electrically photosensitive imaging layers of manifold sets, said layers each being structurally fracturable in response to the combined effect of an applied electrical field and exposure to electromagnetic radiation to which said layer is sensitive, and said sets each comprising one of said imaging layers sandwiched between a donor layer and a receiver layer, at least one of said donor and receiver layers being at least partially transparent to actinic electromagnetic radiation, said imaging performed while the imaging layers of each set are subjected to an electric field, separating each of said sets while said imaging layers are under said electric fields whereby said imaging layer fractures in imagewise configuration to provide positive images on one of said donor and receiver layers, and superimposing said positive images to subtractively synthesize a proof of the image.

2. A method of simultaneously proofing and screen ing color separations made from a natural color original comprising imaging with actinic electromagnetic radiation the blue, green and red separations made from said original through a screen, respectively on yellow, magenta and cyan cohesively weak, electrically photosensitive imaging layers of manifold sets, said layers each being structurally fracturable in response to the combined effect of applied electrical field and exposure to electromagnetic radiation to which said layer is sensitive, and said sets each comprising one of said imaging layers sandwiched between a donor layer and a receiver layer, at least one of said donor and receiver layers being at least partially transparent to actinic electromagnetic radiation, said imaging performed while the imaging layers of each set are subjected to an electric field, separating each of said sets while said imaging layers are under said electric fields whereby said imaging layer fractures in imagewise configuration to provide positive images on one of said donor andreceiver layers and superimposing the screened positive images formed from said manifold sets to subtractively synthesize a proof of the image.

I 3. A method for the simultaneous formation of color separations, separation screening and proofing comprising successively imaging with actinic electromagnetic radiation a colored original on at least yellow, magenta and cyan cohesively weak electrically photosensitive imaging layers of manifold sets, said layers each being structurally fracturable in response to the combined effect of an applied electrical field and exposure to electromagnetic radiation to which said layer is sensitive, and said sets each comprising one of said imaging layers which shows electrophotosensitivity in essentially only that portion of the visible spectrum which is absorbed by that particular imaging layer sandwiched between adonor layer and a receiver layer, at least one of said donor and receiver layers being at least partially transparent to actinic electromagnetic radiation, said imaging performed while the imaging layers of each set are subjected to an' electric field, separating each of said sets while said imaging layers are under said electric fields whereby said imaging layer fractures in imagewise configuration to provide positive images on one of said donor and receiver layers with each of said images being made by exposure through a screen, and superimposing the positive images formed from said manifold sets to subtractively synthesize a proof of the image.

4. The method of claim 1 further including the step of using at least one of the negative and positive images produced from said manifold sets for printing plate preparation.

5. The method of claim 3 further including the step of using at least one of the screened negative images and screened positive images produced from said manifold sets for printing plate preparation.

6. The method of claim 2, further including the step of using at least one of the screened negative images and screened positive images produced from said manifold sets for printing plate preparation.

7. A method according to claim'l further including imaging a black separation from said color image on a black manifold set, using at least one of the black negaformed from said manifold set on the other three positive images to synthesize said proof. I

10. A method according to claim 2 further including the step of exposing a black separation to a'black manifold set through a screen, and superimposing the screened positive manifold image on the other three positives.

11. A method according to claim 2 further including I the step of exposing a black separation'on a black manifold set through a screen, using at least one of the screened black negative images and screened black positive images for the formation of a black printer plate and superimpos ing the screened positive image on the other three positives to subtractively synthesize a proof of the image.

12. A method according to claim 3 further including the step of imaging the colored original on a black manifold set through a screen, using at least one of the screened black negative image and the screened black positive image for the formation of a black printer plate and superimposing the black screened positive manifold image on the other three positives.

References Cited GEORGE F. LESMES, Primary Examiner: J. C. COOPER III, Assistant Examiner Uls.c1. x.R. 96-1, 1.3, .4, 27 V 

